The present invention relates to a bar code scanner for scanning bar codes by an electronically activated image sensor, which is used in such a system that articles of merchandise move together with a record medium (for example, labels or the like) affixed thereto and recorded with the bar codes.
In a conventional apparatus for scanning a light reflected from bar codes or contrastive light reflection pattern by an electronically activated image sensor, it is known that an iris diaphragm is provided for projecting enough illuminance on the bar codes so as to clearly image the bar codes on the light responsive elements of the image sensor, and for controling the focal depth of the bar codes image.
While it is generally arranged that the circular aperture of the iris diaphragm is small so as to prevent the defocus of the image or to increase the focal depth, a luminous intensity reflected from bar codes onto the image sensor is reduced by the small aperture and it is required to employ the light source having a large luminous intensity so as to compensate the reduced luminous intensity.
When the aperture of the iris diaphragm is large so as to increase the luminous intensity projecting on the image sensor, the focal depth is reduced and consequently the scanning accuracy is reduced.